An artificial stone caked from a mixture of a crushed natural stone with a resin or the like is conventionally known. Various ideas have been carried out to make this artificial stone have a design of a natural stone style such as marble or granite and besides superior hardness and strength.
As a trial for improving a function and performance of such an artificial stone, it is proposed to give a luminosity function to the artificial stone with using a luminescent substance such as a noctilucent substance like a light accumulation material or an ultraviolet ray luminescent material emitting light with ultraviolet rays absorption.
For instance, a luminescent tile which consists of an inorganic filler, a synthetic resin, and a light accumulation pigment and includes an inorganic filler of more than about 50% of the total amount, is proposed (Japanese Patent Laid-Open No. 60-137862). For instance, on this luminescent tile, a board of 3 to 5 mm thick is proposed, which is molded and hardened from a composition of; 75 wt % of silica sand as an inorganic filler with an average particle diameter of 0.2 mm or more, 15 wt % of syrup consisting of MMA polymer/MMA monomer of 25/75 in a weight ratio, and 9 wt % of a light accumulation pigment.
In addition, a luminescent material obtained from the following composition is proposed; a natural or synthesized luminescent stone emitting light by ultraviolet rays and an adhesive resin of 4 to 10 wt % against a total amount along with a natural or synthesized aggregate (Japanese Patent Laid-Open No. 8-119706).
However, a luminescent material such as a conventional artificial tile or artificial stone which is made noctilucent, for instance, by the above light accumulation pigment has several hours at most; for sustaining a declining brightness over 3 mcd/m2 which is a lower limit at which a person can ensure a contour of things, from a saturated state after irradiation at 200 Lx with a D65 commonly used light source; and the above proposed material (Japanese Patent Laid-Open No. 60-137862) has only one hour.
In addition, there was a problem that brightness required for a clear visibility which is thought to be necessary for a refuge instruction in a power cut for about 15 minutes was not in an enough level. These problems were common as a problem that enough luminescence performance is not obtained either in case of a light emission by ultraviolet rays.
Furthermore, there was a problem that only a surface layer of 1 mm deep at most from the surface can emit light and a light accumulation material or the like included in a deeper side of a compact of an artificial stone can not act at all, in either a case of an artificial stone (an artificial tile) being made noctilucent by blending a light accumulation pigment or a case of an artificial stone being made luminescent by ultraviolet rays.
For this reason, a thick light emission layer could not be provided. Thus there was a fundamental problem on luminescence performance described above that an extension of an noctilucent time was difficult, for instance, on an noctilucent artificial stone mixed with a light accumulation material.
Actually, owing to these problems, a practical use taking advantage of light accumulation noctilucence which function attracts attention as refuge induction guides in a power cut in an underground shopping center, for instance, is limited to a paint, tape, or a film which includes the light accumulation material.
It is not practical from the view point of a cost to blend a luminescent substance in an artificial stone as parts which do not contribute to a light emission actually, because the noctilucent substance such as a light accumulation material and the luminescent substance with ultraviolet rays are expensive and raise a whole cost of an artificial stone product to 3 to 10 times higher even with a small quantity of addition.
In addition, a conventional artificial stone could not be employed for floor materials, for instance, to which an abrasion resistance is required, as it has a problem not only in the luminescence performance but also in a physical property such as a strength, an abrasion resistance, and weatherability.
Thus, the performance and the use of the conventional artificial stone which is noctiluscent or luminescent with ultraviolet rays were extremely limited.
Considering these situations, the present inventors have proposed an artificial stone; which realizes a high strength and high hardness as an artificial stone including an inorganic aggregate and filler with a resin and a deep hue like a natural stone; allows a light emission with thickness by blending a light accumulation material or an ultraviolet ray luminescent material; enables a contour thickness as an artificial stone to be bigger; and besides enables a luminescent time to be longer (for instance, WO98/39268, WO98/35919).
These proposals are essentially characterized by; using several groups of inorganic materials which average particle diameters are different, in a specific blending ratio; employing transparent inorganic materials for groups with bigger particle diameters; blending light accumulation materials or ultraviolet ray luminescent materials for groups with smaller particle diameters, or coating them beforehand on the surface of the transparent inorganic particles with bigger particle diameters by baking or the like.
And these proposals were based on new findings that it is possible to increase a thickness contributing to a luminosity of a light accumulation material or the like by means of controlling an inner structure of the artificial stone.
Actually, an artificial stone based on the proposal of the present inventors enables brightness of 3 mcd/m2 or more to continue for about 8 hours.
However, after that, the present inventors have investigated as a big subject to control a relationship between a structure of the artificial stone and the luminescence performance; for the purpose of improving the luminescence performance of light accumulation materials and luminescent materials with ultraviolet rays, for raising the initial brightness of light accumulation luminescence and besides enabling the luminosity at a predetermined brightness to continue for a longer time.
It is to realize a light accumulation luminescent artificial stone which shows in maximum non energetic luminescence performance of a predetermined brightness at night or in a power cut and a light emissive artificial stone with ultraviolet rays radiation which shows an energy-saving property in maximum. Besides, concerning on the control, the present inventors have investigated as a subject to sustain and improve a physical property of extremely high quality and high function such as strength, surface hardness, abrasion resistance, weatherability, a color tone, and waterproofing/chemical resistance, for instance, which the present inventors have realized till now.